Interpretive Summary: Vegetable oils can be hydrolyzed to produce free fatty acids which in turn are used to make products such as detergents, shampoos, and lubricants. However, some hydrolysis methods use caustic acids and bases, hazardous solvents and generate waste salt streams. We studied the use of hot pressurized water to hydrolyze cuphea seed oil to produce free fatty acids without acids, bases, or solvents. Optimal conditions for the conversion of cuphea seed oil to free fatty acids were found to be at a pressure of 2000 psi and 350°C. This research provides an effective means to produce free fatty acids for use in chemical manufacturing with minimal waste generation.

Technical Abstract:
Cuphea seed oil (CSO) is a source of medium chain fatty acids for use in chemical manufacturing, including detergents, shampoos and lubricants. Cuphea seed oil is high in decanoic acid and this fatty acid is especially useful in the preparation of estolide biobased lubricants, which have excellent properties, including pour point and cloud point. In order to synthesize these estolides, the decanoic acid must first by hydrolyzed from the CSO. Although this can be accomplished using a catalyst like KOH, followed by neutralization with HCl and finally extraction with hexane, it uses caustic materials, hazardous solvents and generates waste salt streams. This study investigated the use of subcritical water without catalysts for the continuous hydrolysis of CSO. Parameters such as water:cuphea oil ratio; temperature, interaction of pressure and temperature, and flowrate were examined to determine the optimal operating conditions. The optimal water to cuphea oil fatty acid residue was found to be 6:1 and the conversion of the CSO to free fatty acids increased with temperature and leveled off at about 330°C. Hydrolysis increased with pressure, especially between the pressures of 3.4 MPa and 10.3 MPa and the lowest conversions were at the lowest temperature tested (i.e., 300°C). However, the hydrolysis of CSO was slightly better at 350°C than at 365°C at pressures above 10.3 MPa. The conversion was ca. 90% at 350°C and 13.8 MPa. Conversion rates were inversely proportional to flowrate and the best conversions (i.e., 95%) was observed at the lowest flowrates (i.e., 0.25 mL/min). These results demonstrate a continuous subcritical water process method for hydrolyzing CSO to free fatty acids that is effective and requires no catalysts and does not generate a salt waste stream.